Closing the gap on understudied aerosol-climate processes in the rapidly changing central Arctic

Abstract

The accelerated rate of warming in the Arctic is of great concern due to impacts that include thawing permafrost, melting glacial ice, and declining sea ice cover. These processes contribute to amplified warming that affects climate globally. Aerosols, clouds, and fog play a crucial role in regulating sunlight and heat reaching frozen surfaces, but the magnitude of their effects on surface temperature is not well constrained, especially in the central Arctic directly over the sea ice. In addition to directly interacting with radiation, aerosols can serve as seeds or nuclei for cloud formation and alter cloud properties, but even less is known about their impacts and origins. Specifically, aerosols from local pollution, open water including leads and melt ponds, and the snow-covered sea ice surface remain poorly understood, yet could have significant impacts on cloud nuclei concentrations, and thus, central Arctic cloud and fog formation. In order to assess aerosol impacts on clouds and the surface energy budget over the rapidly-shrinking sea ice, collaborative analyses of observations in the central Arctic over the entire annual cycle are essential, particularly given seasonal changes in air mass transport, sunlight, clouds, and sea ice extent.

The 2019 – 2020 Multidisciplinary drifting Observatory for Study of Arctic Climate (MOSAiC) campaign in the provides the unique opportunity to reduce critical knowledge gaps in central Arctic aerosol sources and processes. The overarching objective of the proposed work is to assess understudied aerosol processes associated with aerosol composition and cloud/fog formation in the central Arctic. We will build upon and leverage existing efforts and resources dedicated to measurements of aerosols during MOSAiC. We will focus on processes with the potential for significant impacts on Arctic aerosol composition and clouds, but that have remarkably limited observational understanding in this region, including: (1) aerosols generated from and transformed by ship pollution, (2) emission processes and abundance of coarse-mode aerosol from natural sources (i.e., aerosols greater than 1 μm in diameter), and (3) interactions between aerosols and Arctic fog. Specifically, we frame these as the following scientific research questions we intend to address:

RQ1: What is the evolution and dispersion of ship-based pollution under various atmospheric states in the central Arctic, and how much might it contribute to cloud formation?

RQ2: What are the mechanisms for coarse aerosol generation, including sea salt, biological particles, and dust, and are these important for central Arctic cloud formation?

RQ3: What are the dominant sources of aerosols that facilitate central Arctic fog formation, and how does aerosol composition change during Arctic fog?

The proposed collaborative work involves the use of: (1) existing aerosol, meteorological, oceanographic, and sea ice observations that were collected in real time; (2) existing aerosol data from offline analyses of a subset of discrete aerosol samples collected during the expedition; and (3) new data from additional analyses of aerosol, seawater, sea ice, and snow samples to fill in observational gaps and focus on case studies. By addressing our first research question, we will refine the characterization of ship-based aerosol pollution and gain insights into the impacts of increasing Arctic shipping due to diminishing sea ice. Addressing our second research question will enable a detailed account of coarse aerosol sources and emission mechanisms, which are critical to the population of aerosols that can serve as seeds for cloud ice crystal formation. Our third research question is imperative to answer since central Arctic fog formation and persistence is poorly understood yet could have significant impacts on the energy balance at the sea ice surface. The proposed work involves three female principal investigators (two early-career, one mid-career) and three graduate students contributing to this international collaboration. Overall, the proposed project will enable us to address key scientific Arctic aerosol-cloud questions to better understand the Arctic system science through a holistic approach.